Design of a Steerable Expandable Parallel Clip Applier

Abstract

The upcoming Shaft Actuated Tip Articulated Low Resource Settings (SATA-LRS) platform is in need of a novel design of a strong, foldable beak able to close in parallel. Steerable instruments for minimally invasive surgery (MIS) are used more often but still have some limitations. The end-effectors used are v-shaped, causing tissue that is being clipped to be pushed away or cause peak stresses in the tissue. Many workarounds have been used to avoid these problems, but this project aims to solve the fundamental problem, also taking into account the steerability of the device. V-shaped clips are often limited in size, therefore an expandable u-shaped clip applier is desirable.

AIM: To develop a new type of mechanism able to open and close in parallel in order to apply a u-shaped clip for ligation purposes, which is compatible with the steerable SATA-LRS platform.

METHODS: First, the project definition is chosen, after which the requirements will be formulated and any unknown variables will be experimentally obtained. Then a rigorous morphological analysis will be performed after which the conceptual design is made and the concept selectionis done based on an analytical approach, highly nonlinear FEA-simulations and 5:1 geometrically scaled 3D-printed prototypes to verify the working principles of each of the concepts. The developed concepts will be experimentally validated by means of a test setup.

RESULTS: The designed end-effector allows u-shaped clip with up to 200% increase in size and 400% increase in clip surface area. At a 5mm scale, the expandable beak is able to open just shy of twice the shaft diameter with a span of 9mm, which is close to competing with currently used regular 12mm instruments. The design eliminates limitations currently used v-shapedend-effectors on steerable devices encounter. 50N of clamping force is required, which is three times as much as regular v-shaped gripping. Analytical analysis, FEA simulations and experimental validations show that the device can be made strong enough with a factor of safety of 1.6 and only 0.085mm tip deflection, with an efficiency of 23.1% at a beta angle of 30◦. The device is easily exchangeable on the SATA-LRS platform. A fully functional 5:1 scaled model was successfully made. With minor adjustments to the SATA-LRS, the device can be operated comfortably by any surgeon.

CONCLUSION: This research developed a fully working scaled model of an expandable parallel clip applier, which eliminates the problem regular v-shaped clip appliers have. Also, this system can be mounted to the SATA-LRS and is suitable for steerable instruments. The clips are not limited to the shaft diameter of the device anymore.